/*实现异步日志缓冲区*/

#include "util.cpp"
#include <vector>
#include <cassert>
namespace Mylog
{
    #define DEFAULT_BUFFER_SIZE (100 * 1024 * 1024)
    #define THRESHOLD_BUFFER_SIZE(80 * 1024 * 1024)
    #define INCREMENT_BUFFER_SIZE(10 * 1024 * 1024)
    class Buffer
    {
        public:
            Buffer() : _buffer(DEFAULT_BUFFER_SIZE), _reader_idx(0), _writer_idx(0){}
            //向缓冲区写入数据
            void push(const char *data, size_t len)
            {
                //if(len > writeAbleSize()) return;
                ensureEnoughSize(len);
                std::copy(data, data + len, &_buffer[_writer_idx]);
                moveWriter(len);
            }
            size_t writeAbleSize()//可写空间大小
            {
                return(_buffer.size() - _write_idx);
            }
            //返回可读数据起始地址
            const char* begin()
            {
                return &_buffer[_reader_idx];
            }
            //返回可读数据长度；
            size_t readAbleSize()
            {
                return(_write_idx - _reader_idx);
            }
            void moveReader(size_t len)
            {
                assert(len <= readAbleSize());
                _reader_idx += len;
            }
            //重置读写位置，初始化缓冲区
            void reset()
            {
                _reader_idx = 0;
                _writer_idx = 0;
            }
            //对Buffer实现交换操作
            void swap(Buffer &buffer)
            {
                _buffer.swap(buffer._buffer);
                std::swap(_reader_idx, buffer._reader_idx);
                std::swap(_writer_idx, buffer._writer_idx);
            }
            //判断缓冲区是否为空
            bool empty()
            {
                return (_reader_idx == _writer_idx);
            }
        private:
            void ensureEnoughSize(size_t len)
            {
                if(len <= writeAbleSize()) return;//无需扩容
                size_t new_size = 0;
                if(_buffer.size() < THRESHOLD_BUFFER_SIZE)
                {
                    new_size = _buffer.size() * 2; //小于阈值翻倍增长
                }else{
                    new_size = _buffer.size() + INCREMENT_BUFFER_SIZE;//否则线性增长
                }
                _buffer.resize(new_size);
            }
            //对读写指针进行向后偏移操作
            void moveWriter(size_t len)
            {
                assert((len + _write_idx) <= _buffer.size()); 
                _write_idx += len;
            }
        private:
            std::vector<char> _buffer;
            size_t _reader_idx;//当前可读数据指针
            size_t _writer_idx;//当前可写数据指针
    };
}